Sonatenhauptsatzform means in englisch, first-movement sonata form. The meaning is debatable, but academically it usually refers to an exposition with a main theme (sometimes an introduction), a second theme in the dominant (or relative major if it begins in a minor key); a development which is harmonically unstable and usually breaks up the themes into small pieces; and an exposition that resolves the development and presents the second theme in the main key.
To get from f-sharp minor to g minor, use A major as a pivot chord (III in f#, V/V in g minor).
Walter Ramsey